Apparatus for storing energy generated during breaking of a vehicle and for providing energy to the internal combustion engine of the vehicle at other times

ABSTRACT

A braking and auxiliary driving unit for an internal combustion engine which produces braking and auxiliary motive power by converting electrical energy in both directions between a polyphase AC circuit of a squirrel-cage polyphase induction machine linked to the rotary shaft of the internal combustion engine and the DC circuit of an electricity storage means, the electricity storage means comprises an electrostatic capacitive circuit. A low-voltage storage battery is provided in addition to this electrostatic capacitive circuit, and this can be coupled to the electrostatic capacitive circuit by a bidirectional DC-to-DC converter.

This is a division of application Ser. No. 08/137,196, filed Oct. 22,1993 U.S. Pat. No. 5,513,718.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is utilized in devices which convert mechanical energyproduced during braking of an internal combustion engine into electricalenergy, store this electrical energy, and supply stored electricalenergy to an auxiliary acceleration device when the internal combustionengine is to be accelerated, thereby generating mechanical energy. Inparticular, this invention is utilized in devices in which a rotarysquirrel-cage polyphase induction machine is coupled to a rotary shaftof an internal combustion engine, and in which this squirrel-cagepolyphase induction machine acts as an electric generator during brakingand as an electric motor during acceleration. This invention is a devicewhich is suited to being carried by a motor vehicle equipped with anauxiliary acceleration and auxiliary braking device.

2. Description of the Related Art

The present applicant has disclosed an electric braking and auxiliaryacceleration means for motor vehicles in PCT Publication No. WO88/O6107(PCT Application No. PCT/JP88/00157). As shown in FIG. 12, this deviceis equipped with a squirrel-cage polyphase induction machine 2, therotor of which is directly connected to internal combustion engine 1;storage battery circuit 3 for storing electricity; inverter circuit 4which converts the DC voltage of this storage battery circuit 3 to an ACvoltage of a frequency suitable for inducing a rotating magnetic fieldwith a lower rotational speed than the axial rotational speed ofsquirrel-cage polyphase induction machine 2, and which gives this ACvoltage to squirrel-cage polyphase induction machine 2, and whichconverts AC power from squirrel-cage polyphase induction machine 2 to DCpower; and inverter control circuit 5 which generates control signalswhich set the frequency of the AC-side voltage of this inverter circuit4. This inverter control circuit 5 includes means for generating controlcommands from the driver to suit the operation of the motor vehicle.

Squirrel-cage polyphase induction machine 2 is also fitted with rotationsensor 6, and signals from this rotation sensor 6 are given to invertercontrol circuit 5, to which information from storage battery circuit 3relating to the charge condition of the storage battery is also input.

Capacitor 7 and semiconductor switching circuit 12 are connected to theoutput of inverter circuit 4. Resistor 11 is also connected to theoutput of inverter circuit 4, via this semiconductor switching circuit12. Resistor 11 is constituted in a manner such that it dissipates anyexcess electrical energy which is generated by heavy braking of thevehicle and which cannot be regenerated.

Detection circuit 13 for detecting the output voltage of invertercircuit 4 is also connected to storage battery circuit 3 andsemiconductor switching circuit 12, and current detector 15 is providedat resistor 11 for detecting changes in current. Switching controlcircuit 14 is connected to current detector 15, and controlssemiconductor switching circuit 12 in accordance with its detectionsignals. Detection circuit 13 is connected to this switching controlcircuit 14.

When a motor vehicle equipped with this device brakes, energy generatedby braking is recovered and stored as electrical energy, and when such avehicle accelerates, this stored electrical energy is converted tomechanical energy, thereby supplying auxiliary motive power to theinternal combustion engine which drives the axle.

That is to say, the control circuit which controls the inverter does soin such a manner that in an acceleration mode, in which thesquirrel-cage polyphase induction machine is used as an auxiliarydriving means for the internal combustion engine, the inverter circuitprovides the squirrel-cage polyphase induction machine with a rotatingmagnetic field which has a rotational speed that exceeds the rotationalspeed of the internal combustion engine; while in deceleration mode, inwhich the squirrel-cage polyphase induction machine is used as a brakingdevice for the internal combustion engine, the inverter circuit providesthe squirrel-cage polyphase induction machine with a rotating magneticfield which has a rotational speed which is less than the rotationalspeed of the internal combustion engine. In the acceleration mode, theinverter circuit gives the DC output resulting from the electricalenergy that has been stored in the electricity storage means to thesquirrel-cage polyphase induction machine as a polyphase AC output;while in deceleration mode, it gives the polyphase AC output energy ofthe squirrel-cage polyphase induction machine to the electricity storagemeans as a DC output.

In this previous device, the aforementioned electricity storage means isa storage battery. That is to say, the rated voltage at the DC side ofthe inverter is 200˜300 V, and a storage battery with this rated voltageis obtained by connecting a large number of motor vehicle lead storagebatteries in series.

The applicant has successfully designed and manufactured practicalversions of the aforementioned device and has introduced them on a trialbasis, mainly in buses making regular runs in urban areas. It hastherefore been possible to carry out numerous tests.

The results of these tests have indicated that the device describedabove is an extremely useful device which does not simply dissipate theenergy generated during braking but is able to recover and utilize iteffectively. The results have also shown that this device gives anessentially excellent performance which enables it to be implemented notjust in large motor vehicles, but also more widely in passenger cars andsmall goods vehicles as well. However, it was found that the followingproblems arise when a large lead storage battery is carried on apractical vehicle:

A considerable volume is taken up . . . more specifically, because tenor more series-connected 24 V lead storage batteries are used, the totalvolume is 0.2˜0.4 m².

Vehicle body weight increases . . . more specifically, there is anincrease of 200˜300 kg.

There must be a mounting structure that will provide adequate safety forhuman beings, given that DC electric power of several tens of amperes atvoltages in excess of 200 V will be utilized . . . more specifically, itis necessary to have a safe arrangement of the sort where dangerouselectrical parts are mounted in a secure box provided with a door thatcan be opened and shut, and where the circuits are automaticallyisolated when the door is opened.

Because lead storage batteries are devices that involve chemicalreactions, various maintenance procedures are required. For example, theamount of electrolyte has to be observed under fixed conditions and itsspecific gravity measured, the electrolyte has to be replenished, andsupplementary charging carried out . . . the man-hours involved in suchmaintenance become considerable, and its application to privateautomobiles is difficult.

To give convenient maintenance, all the batteries have to be arranged inone place . . . sufficient space for this cannot be found in a smallvehicle.

There are energy losses due to the internal resistance of the cells . .. this impairs the efficiency with which energy recovered during brakingis utilized during acceleration.

Under ordinary operating conditions, the present storage capacity of thebatteries cannot be detected electrically accurately enough for use inautomatic control . . . although the present storage capacity can befound fairly accurately by measuring the specific gravity of theelectrolyte, sufficient accuracy cannot be guaranteed in measurementswith simple ammeters or voltmeters, due to the aforementioned internalresistance changing with change in temperature, so electrical,measurements cannot be utilized as real-time control information.

The present invention is proposed as a means of solving theaforementioned problems. In other words, the object of this invention isto provide a device which solves the various problems described aboveand which enables the above described principle of good energyutilization efficiency to be widely implemented, even in smaller motorvehicles.

SUMMARY OF THE INVENTION

A distinguishing characteristic of this invention is that it utilizes anelectrostatic capacitive circuit as the electricity storage means. Morespecifically, the electrostatic capacitive circuit can be constituted byconnecting electrically in parallel a plurality of series circuits eachof which comprises a plurality of unit capacitors connected electricallyin series. Because it can be implemented by series and parallelconnections of a plurality of unit capacitors, the electrostaticcapacitive circuit has a plurality of units that are distributed indispersed fashion around various parts of a motor vehicle.

A commercial electric double layer capacitor may be utilized as thespecific implementation of the unit capacitor. Such electric doublelayer capacitors are widely used for backup of electronic circuits, andcapacitors with a breakdown voltage of 2 V and an electrostaticcapacitance of 500 F (farads) are available. Connecting 150 of these inseries gives a breakdown voltage of 300 V, and by further connecting sixof these series circuits in parallel, an assembly with an electrostaticcapacitance of 20 F can be obtained.

This invention can also be constituted in a manner such that a storagebattery with a lower terminal voltage than the DC terminal voltage ofthe aforementioned inverter circuit is connected to the electrostaticcapacitive circuit via a step-up/step-down converter, and thestep-up/step-down converter is controlled by the aforementioned controlcircuits.

Given this arrangement, this invention can be constituted in such mannerthat the inverter control circuit includes the following control modes:

an initial charging mode wherein, with the internal combustion engine ata standstill, the aforementioned electrostatic capacitive circuit ischarged with the energy of the aforementioned storage battery after thevoltage has been stepped up by the step-up/step-down converter;

a starting mode wherein, when the internal combustion engine is beingstarted, energy stored in the electrostatic capacitive circuit is givento the aforementioned squirrel-cage polyphase induction machine as an ACcurrent via the aforementioned inverter circuit, and the squirrel-cagepolyphase induction machine is made to operate as an electric motor;

a deceleration mode wherein, when the vehicle is being braked, thesquirrel-cage polyphase induction machine is made to operate as anelectric generator, and the output AC current of the squirrel-cagepolyphase induction machine is supplied to the aforementionedelectrostatic capacitive circuit as a charging current via theaforementioned inverter circuit; and

an acceleration mode wherein, when the vehicle is being accelerated, thesquirrel-cage polyphase induction machine is made to operate as anelectric motor, and energy stored in the electrostatic capacitivecircuit is supplied via the inverter circuit to the squirrel-cagepolyphase induction machine as an AC current.

The present invention can also be constituted in a manner such that, inaddition to the aforementioned control modes, the control modes include:

a warm-up mode wherein, when the internal combustion engine is warmingup, the squirrel-cage polyphase induction machine is made to operate asan electric generator, and the output AC current of said squirrel-cagepolyphase induction machine is supplied via the inverter circuit to theelectrostatic capacitive circuit as a charging current; and

a supplementary charging mode wherein, when the internal combustionengine is operating and the terminal voltage of the aforementionedelectrostatic capacitive circuit has fallen to or below a prescribedvalue, the squirrel-cage polyphase induction machine is made to operateas an electric generator, and the output AC current of saidsquirrel-cage polyphase induction machine is supplied via the invertercircuit to the electrostatic capacitive circuit as a charging current.

It is desirable for the aforementioned low terminal voltage storagebattery to be rated for the standard electrical equipment of the motorvehicle.

This invention can also be constituted in a manner such that a storagebattery with a lower terminal voltage than the DC terminal voltage ofthe inverter circuit is connected to the electrostatic capacitivecircuit via a bidirectional DC-to-DC converter, and this bidirectionalDC-to-DC converter includes a converter control circuit which controlsthe direction of energy transfer by controlling the switching of theswitching elements in the DC-to-DC converter.

This invention may be constituted in a manner such that the low-voltageside common potential, which constitutes one terminal of theaforementioned storage battery, is isolated from the high-voltage sidecommon potential, which constitutes one terminal of the aforementionedelectrostatic capacitive circuit, and the common potential of theinverter control circuit is connected to the aforementioned high-voltageside common potential, and common potential separation circuitscontaining photocouplers are provided at the control input points of theinverter control circuit.

The aforementioned low-voltage side common potential may be connected tothe potential of the internal combustion engine or the motor vehicle.

The aforementioned converter control circuit may include as its controlmodes:

an initial charging mode, wherein the electrostatic capacitive circuitis charged with the energy of the storage battery after conversion bythe aforementioned DC-to-DC converter; and

a battery charging mode, wherein, when the terminal voltage of theelectrostatic capacitive circuit exceeds a prescribed value, the storagebattery is charged with the stored electrical energy of thiselectrostatic capacitive circuit after conversion by the DC-to-DCconverter.

It is desirable for the invention to have a construction wherein theaforementioned inverter circuit, inverter control circuit andelectrostatic capacitive circuit are encased in an electricallyinsulating material and housed in a metal container connected to thevehicle body potential.

A specific implementation will now be examined. If the breakdown voltageof 300 V is utilized at a rated voltage of 200 V, the rated quantity ofcharge that it is charged with is:

200 V×20 F=4000 coulombs (=ampere seconds)

Using an inverter that is currently being tested:

4000 coulombs/160 amperes=25 seconds

which shows that a 25-second assist is possible given an electric powercorresponding to a maximum current of 160 A at a maximum voltage of 200V. Since the device is not operated continuously at maximum rating, thismeans that a device can be obtained which will work effectively underordinary operating conditions to give continuous deceleration oracceleration of several tens of seconds.

Regarding this exemplification, if 150 unit capacitors each with abreakdown voltage of 2 V and an electrostatic capacitance of 500 F areconnected in series to give a breakdown voltage of 300 V, and six suchseries circuits are further connected in parallel to give an array withan electrostatic capacitance of 20 F, then, since there areapproximately 900 unit capacitors, if these are centralized in oneplace, the actual size will come to approximately the size of aJapanese-style tatami mat (approximately 6ft×3 ft). The weight will be afraction of that of a lead storage battery. Because no maintenance isrequired when an electrostatic capacitive circuit is used, if theoverall size is going to be of this order, the array can be constructedin such manner that it is distributed in dispersed fashion aroundvarious parts of the vehicle and joined with electrical wires.Furthermore, because no maintenance is required, human safety can beensured by sealing the electrostatic capacitive circuit itself inside asecure insulating structure. Also, because there is substantially nointernal resistance in an electrostatic capacitive circuit, there is noloss of stored electrical energy, so that effective energy utilizationis achieved. Moreover, because the quantity of stored charge in anelectrostatic capacitive circuit is proportional to the terminal voltageduring release, the quantity of stored charge can be found accuratelyand in real-time by voltage detection, and this can be utilized directlyfor control purposes.

In tests with this sort of device, the electric charge in theelectrostatic capacitive circuit will eventually self-discharge if thedevice is not used for a long time. There is a similar situation whenthis device is first used after manufacture, since no charge has beenstored in the electrostatic capacitive circuit. Now, it is impossible tostart the internal combustion engine when there is hardly any chargestored in the electrostatic capacitive circuit.

To remedy this, to provide an electrostatic capacitive circuit directlyconnected to the DC side of the inverter circuit is provided as thestorage means, plus a storage battery with a lower voltage than thisDC-side voltage likewise is connected to this DC side via astep-up/step-down converter.

If a vehicle which has this device is equipped with a storage battery(terminal voltage 24 V or 12 V), the energy of this storage battery canbe utilized when there is hardly any stored charge in the electrostaticcapacitive circuit, i.e., either directly after manufacture of thedevice or when it has not been used for a Considerable length of time.

In the initial charging mode, the step-up/step-down converter is used togenerate high voltage pulses from the terminal voltage of this storagebattery, thereby causing some charge to be stored in the electrostaticcapacitive circuit.

In starting mode, the internal combustion engine is started by utilizingelectric charge that has been stored in this initial charging mode tomake the squirrel-cage polyphase induction machine operate as anelectric motor.

When the internal combustion engine is revolving under its own power,electric power is extracted from the squirrel-cage polyphase inductionmachine and electric charge once again is stored in the electrostaticcapacitive circuit. It is desirable for this to be a special form ofcontrol for a warm-up mode. The electrostatic capacitive circuit reachesits rated terminal voltage in this warm-up mode.

The motor vehicle is now able to go. In acceleration mode, electriccharge that has been stored in the electrostatic capacitive circuit isdischarged and the squirrel-cage polyphase induction machine used forauxiliary motive power. In deceleration mode, electrical energygenerated by the squirrel-cage induction machine is stored in theelectrostatic capacitive circuit.

If the acceleration mode is used too much so that and the quantity ofcharge stored in the electrostatic capacitive circuit is less than aprescribed value, the control mode is changed to supplementary chargingmode and the squirrel-cage polyphase induction machine is made tooperate as an electric generator. Accordingly, provided that theinternal combustion engine is rotating, the quantity of electric chargestored in the electrostatic capacitive circuit can always be maintainedat or above a prescribed value.

With this device, when there is plentiful stored electric charge in theelectrostatic capacitive circuit, the low terminal voltage storagebattery can be maintained in a charged condition by controlling thestep-up/step-down converter so as to generate a low voltage. Charging ofthe storage battery need not be by this method, and it is also feasiblefor it to be charged by means of an alternator of the sortconventionally fitted to internal combustion engines.

Given a constitution wherein an alternator is utilized in this manner,the aforementioned step-up/step-down converter :can be a simple step-upconverter. In such a case, the step-up converter can be a DC-to-DCconverter, which is well known as a power supply device.

An explanation will now be given of the case where a bidirectionalDC-to-DC converter is utilized. In the initial charging mode, thebidirectional DC-to-DC converter is used to generate a high voltage fromthe terminal voltage of the storage battery, thereby causing some chargeto be stored in the electrostatic capacitive circuit. In starting mode,the internal combustion engine is started by utilizing electric chargethat has been stored during this initial charging mode to make thesquirrel-cage polyphase induction machine operate as an electric motor.When the internal combustion engine is revolving under its own power,electric power is extracted from the squirrel-cage polyphase inductionmachine and electric charge once again storm in the electrostaticcapacitive circuit. It is desirable for this to be a special form ofcontrol for a warm-up mode. The electrostatic capacitive circuit reachesits rated terminal voltage in this warm-up mode.

The motor vehicle is now able to go. In acceleration mode, electriccharge that has been stored in the electrostatic capacitive circuit isdischarged and the squirrel-cage polyphase induction machine used forauxiliary motive power. In deceleration mode, electrical energygenerated by the squirrel-cage polyphase induction machine is stored inthe electrostatic capacitive circuit.

If has been used too much, the acceleration mode and the quantity ofcharge stored in the electrostatic capacitive circuit is less than aprescribed value, the control mode is changed to supplementary chargingmode and the squirrel-cage polyphase induction machine made to operateas an electric generator. Accordingly, provided that the internalcombustion engine is rotating, the quantity of electric charge stored inthe electrostatic capacitive circuit can always be maintained at orabove a prescribed value.

With this device, when there is plentiful storm electric charge in theelectrostatic capacitive circuit, the inverter control circuit cansteadily maintain the storage battery in a charged condition bycontrolling the bidirectional DC-to-DC converter so as to generate a lowvoltage.

With a device according to this invention, the common potential can beseparated into a high-voltage side and a low-voltage side. Thelow-voltage side is then common with the general load circuit of themotor vehicle and the common potential is connected to the vehicle bodypotential. In other words, a device according to this invention enablesthe low-voltage side and high-voltage side common potentials to beseparated by means of the transformer in the bidirectional DC-to-DCconverter. On the high-voltage side, the common potential is notconnected to the vehicle body and is therefore floating with respect tovehicle body potential. Accordingly, if for any reason a human body wereto come into contact with a high-voltage circuit, no electric shockwould immediately be received, and danger could be avoided.

In the case of the various control inputs to the inverter controlcircuit (e.g., sensor inputs and driver-manipulated inputs), the commonpotentials are separated by common potential separation circuits and thesignals are transmitted by means of photocouplers. The common potentialof the inverter control circuit can therefore be connected to the commonpotential of the inverter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the constitution of a first embodimentof this invention;

FIG. 2 shows an example of the constitution of the electrostaticcapacitive circuit in the first embodiment of this invention;

FIG. 3 is a block diagram showing the overall constitution of a secondembodiment of this invention;

FIG. 4 is a block diagram showing the constitution of thestep-up/step-down converter and the inverter circuit in the secondembodiment of this invention.

FIG. 5 and FIG. 6 are flowcharts showing the flow of control actions ofthe inverter control circuit in the second and third embodiments of thisinvention;

FIG. 7 shows the flow for control of charging and discharging of theelectrostatic capacitive circuit in the second and third embodiments ofthis invention;

FIG. 8 is a block diagram showing the overall constitution pertaining toa third embodiment of this invention;

FIG. 9 is a block diagram of an electrical system showing theconstitution of the third embodiment of this invention;

FIG. 10 is a circuit diagram showing the constitution of thebidirectional DC-to-DC converter in the third embodiment of thisinvention; FIG. 11a is a circuit diagram showing the constitution of acommon potential separation circuit for control inputs in the thirdembodiment of this invention, and FIG. 11b is a circuit diagram showingthe constitution of a common potential separation circuit for outputs;and

FIG. 12 is a block diagram showing a constitution according to the priorart.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The following is a listing of the components of the present inventionillustrated in the figures and the reference numerals associatedtherewith

1 . . . internal combustion engine; 2 . . . squirrel-cage polyphaseinduction machine; 3 . . . storage battery circuit; 4 . . . invertercircuit; 5 . . . inverter control circuit; 6 . . . rotation sensor; 7 .. . capacitor; 11 . . . resistor; 12 . . . semiconductor switchingcircuit; 13 . . . detection circuit; 14 . . . switching control circuit;15 . . . current detector; 19 . . . bidirectional DC-to-DC converter; 20. . . electrostatic capacitive circuit; 21 . . . step-up/step-downconverter; 22 . . . storage battery; 24 . . . converter control circuit;25 . . . common potential separation circuit for control input; 25a, 26a. . . photocouplers; 26 . . . common potential separation circuit foroutput; 25b, 26b . . . filters; 26c . . . relay; 26d . . . switch; 26e .. . diode; 26f . . . resistor; 30 metal container; 31a, 31b . . .low-voltage side terminals; 31c, 31d . . . high-voltage side terminals;32 . . . low-voltage windings; 33 . . . high-voltage windings; 35 . . .transformer; Da, Db . . . low-voltage side rectifying elements; Dc, Dd.. . high-voltage side rectifying elements; Ta, Tb . . . low-voltage sideswitching elements; Tc, Td . . . high-voltage side switching elements;V1 . . . low-voltage side voltage detection circuit; V2 . . .high-voltage side voltage detection circuit; I1 . . . low-voltage sidecurrent detection circuit; I2 . . . high-voltage side current detectioncircuit.

EMBODIMENTS

Embodiments of this invention will now be explained on the basis of thedrawings. FIG. 1 is a block diagram showing the constitution of a firstembodiment of this invention.

A device according to the first embodiment has an electrostaticcapacitive circuit as the electricity storage means. In addition, justas in the case of the prior art, a device according to the firstembodiment has squirrel-cage polyphase induction machine 2, the rotor ofwhich is directly connected to internal combustion engine 1; invertercircuit 4 which converts the DC voltage of electrostatic capacitivecircuit 20 to an AC voltage of a frequency suitable for inducing arotating magnetic field with a rotational speed which is lower than orhigher than the axial rotational speed of squirrel-cage polyphaseinduction machine 2, and which gives this AC voltage to squirrel-cagepolyphase induction machine 2, or which converts the AC power fromsquirrel-cage polyphase induction machine 2 to DC power; and invertercontrol circuit 5 which generates control signals that set the frequencyof the AC-side voltage of this inverter circuit 4. This inverter controlcircuit 5 includes means for generating control commands from the driverto suit the operation of the motor vehicle.

Squirrel-cage polyphase induction machine 2 is also fitted with rotationsensor 6, and signals from this rotation sensor 6 are given to invertercontrol circuit 5, to which information relating to the chargingcondition of electrostatic capacitive circuit 20 is also input.

Capacitor 7 and semiconductor switching circuit 12 are connected to theoutput side of inverter circuit 4. Resistor 11 is also connected to theoutput side of inverter circuit 4, via this semiconductor switchingcircuit 12. This resistor 11 dissipates any excess electrical energywhich is generated by heavy braking of the vehicle and which cannot beregenerated.

Detection circuit 13 for detecting the output voltage of invertercircuit 4 is also connected to electrostatic capacitive circuit 20 andsemiconductor switching circuit 12, and current detector 15 is providedat resistor 11 for detecting changes in current. Switching controlcircuit 14 is connected to this current detector 15 and controlssemiconductor switching circuit 12 in accordance with its detectionsignals. Detection circuit 13 is connected to this switching controlcircuit 14.

Inverter control circuit 5 also includes a means for controllinginverter circuit 4 in a manner such that in acceleration mode, in whichsquirrel-cage polyphase induction machine 2 is used as an auxiliarydriving means for internal combustion engine 1, a rotating magneticfield with a velocity which exceeds the rotational speed of internalcombustion engine 1 is given to squirrel-cage polyphase inductionmachine 2, while in deceleration mode, in which squirrel-cage polyphaseinduction machine 2 is used as a braking device for internal combustionengine 1, a rotating magnetic field with a velocity that is less thanthe rotational speed of internal combustion engine 1 is given tosquirrel-cage polyphase induction machine 2. Inverter circuit 4 includesa circuit means which, in the aforementioned acceleration mode, givesthe DC output resulting from the electrical energy that has been storedin electrostatic capacitive circuit 20 to squirrel-cage polyphaseinduction machine 2 as a polyphase AC output; and in deceleration mode,gives the polyphase AC output energy of the squirrel-cage polyphaseinduction machine to electrostatic capacitive circuit 20 as a DC output.

As shown in FIG. 2, which depicts one exemplification, electrostaticcapacitive circuit 20 is an array of 900 capacitors in total. These arearranged in series circuits, each of which comprises 150 unit capacitorsC₁, C₂, . . . C₁₅₀ of identical electrostatic capacitance (500 F, 2 V)connected electrically in series. Six such series circuits are thenconnected in parallel.

Resistances R₁, R₂, R₃, . . . R₁₅₀ of identical resistance value arerespectively connected in parallel across each of these capacitors, andeach of the resulting six lines of resistances is connected in series.

Resistances are arranged in this manner for the following reason. Eventhough each capacitor has the same nominal electrostatic capacitance,manufacturing tolerances are such that there is some--albeitslight--variation in actual capacitance value, with the result thatthere will be differences in the terminal voltage generated across thecapacitors. To prevent this, resistances (which exhibit littlemanufacturing variation) are connected in parallel across each capacitorto make the generated terminal voltages as uniform as possible. Theseresistances R₁, R₂, R₃, . . . R₁₅₀ can be omitted if manufacturingvariations in the capacitors have been reduced.

In this exemplification, as described above, 900 of the capacitors andresistances are used. If these are arranged in a plane, the resultingarray has approximately the dimensions of one tatami mat, i.e., 900mm×1800 mm in area and 45 mm thick. However, once the series-connectedgroups of capacitors and resistances have been connected electrically,they can be distributed in dispersed fashion in spaces within thevehicle that are not being utilized. Accordingly, there need be noreduction in useable space, and such an array can be made much lighterthan a conventional battery.

Although 900 capacitors and resistances were used in the exampledescribed above, this is not a necessary restriction, and the number canbe set freely to suit each type of vehicle.

For example, some commercial electric double layer capacitors have abreakdown voltage of 2 V and an electrostatic capacitance of 500 F. If150 of these are connected in series, the breakdown voltage becomes 300V, and if six such circuits are connected in parallel, an electrostaticcapacitance of 20 F is obtained.

If the breakdown voltage of 300 V is utilized at a rated voltage of 200V, the rated quantity of charge that it is charged with is:

200 V×20 F=4000 coulombs (=ampere seconds)

With the inverter that is currently being used, the maximum current is160 A, so:

4000 coulombs/160 amperes=25 seconds

which means that auxiliary motive power can be supplied for 25 secondsgiven an electric power corresponding to a maximum current of 160 A at amaximum voltage of 200 V.

An explanation will now be given of the operation of the embodiment ofthis invention so constituted.

First of all, when a braking force is to be generated in the rotarysystem, inverter control circuit 5 generates control signals such that arotating magnetic field with a lower velocity than the rotational speedof the rotor of squirrel-cage polyphase induction machine 2, as detectedby rotation sensor 6, is given to the stator of squirrel-cage polyphaseinduction machine 2. In this situation, squirrel-cage polyphaseinduction machine 2 operates as an electric generator and the electricalenergy generated is converted to DC energy by inverter circuit 4 andsupplied to electrostatic capacitive circuit 20 as a charging current.When braking torque is so large that electrostatic capacitive circuit 20cannot completely absorb this DC energy, the DC terminal voltageincreases until it exceeds a prescribed value, whereupon semiconductorswitching circuit 12 detects this and closes, so that resistor 11 isconnected across the terminals of electrostatic capacitive circuit 20.

On the other hand, when a driving force is to be given to the rotarysystem, inverter control circuit 5 generates control signals such that arotating magnetic field with a higher velocity than the rotational speedof the rotor of squirrel-cage polyphase induction machine 2, as detectedby rotation sensor 6, is given to the stator of squirrel-cage polyphaseinduction machine 2. In this situation, DC current is extracted fromelectrostatic capacitive circuit 20, converted by inverter circuit 4 toa polyphase alternating current suitable for the rotating magneticfield, and supplied to squirrel-cage polyphase induction machine 2.

Both braking torque and driving force increase with increasingdifference between the rotational speed of the rotating magnetic fieldand the axial rotational speed. In this embodiment, the ratio betweenthis difference and the rotational speed of the rotating magneticfield--in other words, the slip of squirrel-cage polyphase inductionmachine 2--is restricted to ±10%.

An explanation will now be given of how-the charging of electrostaticcapacitive circuit 20 is controlled. Control signals for giving arotating magnetic field to the stator of squirrel-cage polyphaseinduction machine 2, wherein the rotating magnetic field corresponds tothe rotation of the rotor of said induction machine, are supplied toinverter circuit 4 from inverter control circuit 5. Rotation informationfrom rotation sensor 6 and information relating to the state of chargingof electrostatic capacitive circuit 20 are input to this invertercontrol circuit 5. Inverter control circuit 5 contains a microprocessorand a means whereby operating control signals (which will changeaccording to the driving situation) are introduced as a result ofcontrol action by the driver.

As well as being able to give the energy of the DC-side terminals to theAC-side terminals as described above, inverter circuit 4 can give energygenerated at the AC-side terminals to the DC-side terminals. Moreover,by using inverter control circuit 5 to control the rotational speed ofthe rotating magnetic field so that squirrel-cage polyphase inductionmachine 2 becomes an electric motor, a .driving force can be given tothe rotary shaft of squirrel-cage polyphase induction machine 2, therebymaking the induction machine operate as an auxiliary driving means forinternal combustion engine 1. Electrical energy charged in electrostaticcapacitive circuit 20 is used under these circumstances.

As long as the internal combustion engine is rotating, charging ofelectrostatic capacitive circuit 20 by the electric generator coupled tothe internal combustion engine is continued. If stored energy resultingfrom charging is used due to operation of a starter motor or auxiliaryequipment, the charging of electrostatic capacitive circuit 20 iscontrolled so that it reaches a fully charged state equivalent to itsrated charged capacity in as short a time as possible.

FIG. 3 is a block diagram showing the overall constitution of a secondembodiment of this invention, and FIG. 4 is a block diagram showing theconstitution of the step-up/step-down converter and the inverter circuitin this second embodiment.

The distinguishing characteristics of the second embodiment shown inFIG. 3 are that it contains an electrostatic capacitive circuit 20,which is directly connected to the DC side of inverter circuit 4, and astorage battery 22, which is connected to this electrostatic capacitivecircuit 20 via step-up/step-down converter 21 and which has a lowerterminal voltage than the DC terminal voltage of inverter circuit 4, andstep-up/step-down converter 21 is controlled by inverter control circuit5.

FIG. 4 shows the constitution of this second embodiment, focusingparticularly on the electrical system. Identical constituent elementshave been given identical numbers and can be understood in the same way.Detailed explanations of such identical parts will therefore be omitted.

The control modes of inverter .control circuit 5 include an initialcharging mode wherein, with internal combustion engine 1 at standstill,electrostatic capacitive circuit 20 is charged with the energy ofstorage battery 22 after the voltage has been stepped up bystep-up/step-down converter 21; a starting mode wherein, when internalcombustion engine 1 is being started, energy stored in electrostaticcapacitive circuit 20 is given to squirrel-cage polyphase inductionmachine 2 as an AC current via inverter circuit 4, and squirrel-cagepolyphase induction machine 2 is made to operate as an electric motor; adeceleration mode wherein, when the vehicle is being braked,squirrel-cage polyphase induction machine 2 is made to operate as anelectric generator, and the output AC current of squirrel-cage polyphaseinduction machine 2 is supplied to electrostatic capacitive circuit 20as a charging current via inverter circuit 4; an acceleration modewherein, when the vehicle is being accelerated, squirrel-cage polyphaseinduction machine 2 is made to operate as an electric motor, and energystored in electrostatic capacitive circuit 20 is supplied via invertercircuit 4 to squirrel-cage polyphase induction machine 2 as an ACcurrent; a warm-up mode wherein, when the internal combustion engine iswarming up, squirrel-cage polyphase induction machine 2 is made tooperate as an electric generator, and the output AC current ofsquirrel-cage polyphase induction machine 2 is supplied via invertercircuit 4 to electrostatic capacitive circuit 20 as a charging current;and a supplementary charging mode wherein, when internal combustionengine 1 is operating and the terminal voltage of electrostaticcapacitive circuit 20 has fallen to or below a prescribed value,squirrel-cage polyphase induction machine 2 is made to operate as anelectric generator, and the output AC current of squirrel-cage polyphaseinduction machine 2 is supplied via inverter circuit 4 to electrostaticcapacitive circuit 20 as a charging current. The terminal voltage ofstorage battery 22 is set at the rated voltage of standard electricalequipment for motor vehicles. Electrostatic capacitive circuit 20 isidentical to the one that was explained above with regard to the firstembodiment.

An explanation will now be given of the operation of the secondembodiment of this invention thus constituted. Its ordinary operationswill be passed over, since these are identical to those of theaforementioned first embodiment, and an explanation will be given of howthe charging of electrostatic capacitive circuit 20 is controlled.

Control signals for giving a rotating magnetic field to the stator ofsquirrel-cage polyphase induction machine 2, the rotating magnetic fieldcorresponding to the rotation of the rotor of the induction machine, aresupplied to inverter circuit 4 from inverter control circuit 5. Rotationinformation from rotation sensor 6 and information relating to the stateof charging of electrostatic capacitive circuit 20 are input to thisinverter control circuit 5. Inverter control circuit 5 contains amicroprocessor and a means whereby operating control signals (which willchange according to the driving situation) are introduced as a result ofcontrol action by the driver.

As well as being able to give the energy of the DC-side terminals to theAC-side terminals as described above, inverter circuit 4 can give energygenerated at the AC-side terminals to the DC-side terminals. Moreover,by using inverter control circuit 5 to control the rotational speed ofthe rotating magnetic field so that squirrel-cage polyphase inductionmachine 2 becomes an electric motor, a driving force can be given to therotary shaft of squirrel-cage polyphase induction machine 2, therebymaking said induction machine operate as an auxiliary driving means forinternal combustion engine 1. Electrical energy charged in electrostaticcapacitive circuit 20 is used under these circumstances.

As long as internal combustion engine 1 is rotating, charging ofelectrostatic capacitive circuit 20 by the electric generator coupled tointernal combustion engine 1 is continued. If the stored energyresulting from charging is used due to operation of a starter motor orauxiliary equipment, the charging of electrostatic capacitive circuit 20is controlled so that it reaches a fully charged state equivalent to itsrated charged capacity in as short a time as possible.

An explanation will now be given of how the charging and discharging ofelectrostatic capacitive circuit 20 is controlled in embodiments of thisinvention.

FIG. 5 and FIG. 6 explain the operating modes of this second embodiment.FIG. 7 shows the flow for control of charging and discharging of theelectrostatic capacitive circuit in the second embodiment.

When there is hardly any stored electric charge in electrostaticcapacitive circuit 20, which is the case directly after manufacture ofthe device or when the device has not been in use for a long time,initial charging mode is selected and the electrostatic capacitivecircuit is charged by the step-up chopper in step-up/step-down converter21 to a minimum voltage of 15.0 V. (See 1 in FIG. 7. Identical controlsteps in FIG. 5 and FIG. 6 are assigned the same numbers.) If startingmode is selected and internal combustion engine 1 is started by means ofthis voltage, the voltage drops to approximately 100 V (2).

When internal combustion engine 1 starts and begins to warm up, awarm-up mode is selected, squirrel-cage polyphase induction machine 2begins to generate electricity, electric charge is stored inelectrostatic capacitive circuit 20, and the rated voltage of 350 V isreached (3). The motor vehicle is now able to go. When acceleration modeis selected while travelling, electric charge stored in electrostaticcapacitive circuit 20 is discharged and squirrel-cage polyphaseinduction machine 2 is used for auxiliary motive power (4).Alternatively, when deceleration mode is selected while travelling,squirrel-cage polyphase induction machine 2 is used for supplementarycharging (5).

If acceleration mode is used for a long period of time, the voltagedrops, and when it falls below a lower limit voltage which has been setat approximately 230 V, selection of acceleration mode is prohibited. Ifit reaches the minimum voltage, the control mode changes over tosupplementary charging mode, squirrel-cage polyphase induction machine 2is made to operate as an electric generator, and electrostaticcapacitive circuit 20 is slowly charged (6). Thus, as long as internalcombustion engine 1 is rotating, the quantity of charge stored inelectrostatic capacitive circuit 20 is always maintained at or above aprescribed value. Thereafter, the same control is repeated.

Control of the charging and discharging of electrostatic capacitivecircuit 20 will now be explained following the steps set out in FIG. 5and FIG. 6. When the starting key switch is set to ON, it is decidedwhether or not capacitor voltage V_(c) of electrostatic capacitivecircuit 20 is greater than 150 V. If it is at or below 150 V, initialcharging mode 1 is selected, the step-up chopper is operated andcharging carried out. If it is above 150 V, operation of the step-upchopper is stopped and it is decided whether or not the rotational speedN_(E) of internal combustion engine 1 exceeds 350 rpm.

If it does not exceed 350 rpm, it is decided whether the starting keyswitch is ON or OFF, and if internal combustion engine 1 has beenstarted, processing returns again to the decision as to whether or notits rotational speed N_(E) exceeds 350 rpm. If internal combustionengine 1 has not been started, the starting key switch is closed,cranking carried out, and processing returns to the decision as towhether or not the rotational speed N_(E) of internal combustion engine1 exceeds 350 rpm.

If the rotational speed N_(E) of internal combustion engine 1 doesexceed 350 rpm at this processing step, the cranking action which wasapplied as a result of the starting key switch being closed is stoppedand, since the engine is now warming up, warm-up charging mode 3 isselected. Next, it is decided whether or not capacitor voltage V_(c) ofelectrostatic capacitive circuit 20 exceeds 230 V. If it is less than230 V, supplementary charging mode 7 is selected, squirrel-cagepolyphase induction machine 2 is made to operate as an electricgenerator, and it is decided whether or not the capacitor voltage V_(c)exceeds 350 V. If it does not exceed this value, the control flowreturns to generation of electricity in supplementary charging mode 7,and these processing steps are repeated until 350 V is reached. If 350 Vis exceeded, the generation of electricity by squirrel-cage polyphaseinduction machine 2 is stopped.

Continuing on from this, it is decided whether or not the acceleratorpedal voltage (a voltage indicating the displacement of the acceleratorpedal) is greater than the assist start-up voltage. If it is greaterthan the assist start-up voltage, it is decided again whether or not thevoltage V_(c) exceeds 200 V. If it does not exceed 200 V, the controlflow returns to the decision as to whether or not the accelerator pedalvoltage is greater than the assist start-up voltage. If it does exceed200 V, the drive assist mode can be selected. In drive assist mode,energy that has been stored in electrostatic capacitive circuit 20 isgiven via inverter circuit 4 to squirrel-cage polyphase inductionmachine 2 as an assist voltage, thereby providing supplementary torquefor the drive assist. Thereafter, the same control is repeated.

If the accelerator pedal voltage is not greater than the assist start-upvoltage, it is decided whether or not this accelerator pedal voltage isan idling voltage (a voltage indicating that the accelerator pedal isnot being pressed). If it is not an idling voltage, it is decidedwhether or not the voltage V_(c) is less than 150 V.

If V_(c) is above 150 V, the control flow returns to the decision as towhether or not the accelerator pedal voltage is greater than the assiststart-up voltage. If V_(c) is less than 150 V, supplementary chargingmode is selected and it is decided whether or not the capacitor voltageV_(c) exceeds 230 V. If it does not exceed 230 V, the control flowreturns to the decision as to whether or not the accelerator pedalvoltage is greater than the assist start-up voltage. If V_(c) doesexceed 230 V, generation of electricity by squirrel-cage polyphaseinduction machine 2 is stopped.

If it has been decided that the accelerator pedal voltage is an idlingvoltage, it is decided whether or not the switch of squirrel-cagepolyphase induction machine 2 is ON. If it is ON, supplementary chargingmode is selected and it is decided whether or not capacitor voltageV_(c) exceeds 400 V, which is the regeneration shutdown voltage. If itdoes, capacitor voltage V_(c) is controlled so that it does not exceedthis voltage, and the aforementioned processing operations are repeated.If V_(c) does not exceed the regeneration shutdown voltage, the positionof the operating lever of squirrel-cage polyphase induction machine 2 isset to a position that satisfies the capacitor current I_(c).Thereafter, the aforementioned processing operations are repeated.

If the switch of squirrel-cage polyphase induction machine 2 is not ON,it is decided whether or not the rotational speed of internal combustionengine 1 exceeds 700 rpm. If it does exceed this value, supplementarycharging is carried out and it is decided whether or not capacitorvoltage V_(c) is below 400 V. If it is below 400 V, generation ofelectricity is stopped. If V_(c) exceeds 400 V, the control flow returnsto the decision as to whether or not the accelerator pedal voltage isgreater than the assist start-up voltage, and thereafter the sameprocessing operations as described above are repeated.

If the rotational speed N_(E) of internal combustion engine 1 is below700 rpm, there is a changeover to idling electricity generation mode 6,and it is decided whether or not capacitor voltage V_(c) is greater than230 V. If it is less than 230 V, the Control flow returns to thebeginning. If V_(c) exceeds 230 V, generation of electricity bysquirrel-cage polyphase induction machine 2 is stopped.

An explanation will now be given of a third embodiment of thisinvention. FIG. 8 is a block diagram showing the overall constitution ofthis third embodiment; FIG. 9 is a block diagram of the electricalsystem showing the constitution of the third embodiment; FIG. 10 is acircuit diagram showing the constitution of the bidirectional DC-to-DCconverter in this embodiment of the invention; FIG. 11a is a circuitdiagram showing the constitution of a common potential separationcircuit for control inputs in this embodiment of the invention; and FIG.11b is a circuit diagram showing the constitution of a common potentialseparation circuit for outputs.

As shown in FIG. 8 or FIG. 9, this third embodiment has a storage meanswhich includes high-voltage electrostatic capacitive circuit 20 directlyconnected to the DC side of inverter circuit 4; storage battery 22 witha low voltage equal to the rated voltage of ordinary electricalequipment for motor vehicles; and bidirectional DC-to-DC converter 19which is connected between electrostatic capacitive circuit 20 andstorage battery 22. Bidirectional DC-to-DC converter 19 includes theconverter control circuit 24 shown in FIG. 10, and this controls thedirection of energy transfer by controlling the switching of theswitching elements in the DC-to-DC converter.

The low-voltage side common potential which constitutes one terminal ofstorage battery 22 is isolated from the high-voltage side commonpotential which constitutes one terminal of electrostatic capacitivecircuit 20; the common potential of inverter control circuit 5 isconnected to the high-voltage side common potential; common potentialseparation circuits 25 for control inputs are provided at the controlinput points of inverter control circuit 5, said separation circuitscontaining photocouplers 25a; common potential separation circuits 26for outputs are provided at the control output points of invertercontrol circuit 5, said separation circuits containing photocouplers26a; and the low-voltage side common potential is connected to thevehicle body potential.

The control modes of converter control circuit 24 include an initialcharging mode wherein electrostatic capacitive circuit 20 is Chargedwith energy of storage battery 22 after conversion by bidirectionalDC-to-DC converter 19; and a battery-charging mode wherein, when theterminal voltage of electrostatic capacitive circuit 20 exceeds aprescribed value, storage battery 22 is charged with stored electricalenergy from this electrostatic capacitive circuit 20 after conversion bybidirectional DC-to-DC converter 19. The control modes of invertercontrol circuit 5 include a starting mode wherein energy stored inelectrostatic capacitive circuit 20 is given to squirrel-cage polyphaseinduction machine 2 as an AC current via inverter circuit 4, andsquirrel-cage polyphase induction machine 2 is made to operate as anelectric motor; a deceleration mode wherein, when the vehicle is beingbraked, squirrel-cage polyphase induction machine 2 is made to operateas an electric generator, and the output AC current of squirrel-cagepolyphase induction machine 2 is supplied via inverter circuit 4 toelectrostatic capacitive circuit 20 as a charging current;an-acceleration mode wherein; when the vehicle is being accelerated,squirrel-cage polyphase induction machine 2 is made to operate as anelectric motor, and energy stored in electrostatic capacitive circuit 20is supplied via inverter circuit 4 to squirrel-cage polyphase inductionmachine 2 as an AC current; a warm-up mode, wherein, following on fromthe starting mode and while internal combustion engine 1 is warming up,squirrel-cage polyphase induction machine 2 is made to operate as anelectric generator, and the output AC current of squirrel-cage polyphaseinduction machine 2 is supplied via inverter circuit 4 to electrostaticcapacitive circuit 20 as a charging current; and a supplementarycharging mode wherein, when internal combustion engine 1 is operatingand the terminal voltage of electrostatic capacitive circuit 20 hasfallen to or below a prescribed value, squirrel-cage polyphase inductionmachine 2 is made to operate as an electric generator, and the output ACcurrent of squirrel-cage polyphase induction machine 2 is supplied viainverter circuit 4 to electrostatic capacitive circuit 20 as a chargingcurrent. Inverter circuit 4, inverter control circuit 5 andelectrostatic capacitive circuit 20 are encased in an electricallyinsulating material and housed in metal container 30 connected to thevehicle body potential.

As shown in FIG. 10, which depicts one example, bidirectional DC-to-DCconverter 19 has low-voltage side terminals 31a and 31b; high-voltageside terminals 31c and 31d; transformer 35 comprising low-voltagewindings 32 and high-voltage windings 33; low-voltage side switchingelements Ta and Tb inserted between low-voltage windings 32 andlow-voltage terminals 31a and 31b respectively; high-voltage sideswitching elements Tc and Td inserted between high-voltage windings 33and high-voltage side terminals 31c and 31d respectively; low-voltageside rectifying elements Da and Db connected in parallel acrosslow-voltage side switching elements Ta and Tb, respectively;high-voltage side rectifying elements Dc and Dd connected in parallelacross high-voltage side switching elements Tc and Td, respectively; andconverter control circuit 24 which controls low-voltage side switchingelements Ta and Tb and high-voltage side switching elements Tc and Td.Converter control circuit 24 has a control means whereby, inlow-voltage-to,high-voltage conversion mode, switching control signalsare given to low-voltage side switching elements Ta and Tb, andhigh-voltage side switching elements Tc and Td are kept open; and acontrol means whereby, in high-voltage-to-low-voltage conversion mode,switching control signals are given to high-voltage side switchingelements Tc and Td, and low-voltage side switching elements Ta and Tbare kept open; and a selection means that selects one or other of thetwo control modes.

There are also provided low-voltage side detection circuit V1 whichdetects the terminal voltage across low-voltage side terminals 31a and31b, and high-voltage side voltage detection circuit V2 which detectsthe terminal voltage across high-voltage side terminals 31c and 31d.Converter control circuit 24 also includes a means whereby theaforementioned selection means is automatically controlled by fetchingthe respective detection outputs of these two voltage detection circuitsV1 and V2 during starting, and comparing these two detection outputswith respective reference values. There are also provided low-voltageside current detection circuit I1 which detects the current inlow-voltage windings 32 and high-voltage side current detection circuitI2 which detects the current in high-voltage windings 33. Convertercontrol circuit 24 also has a means whereby the detection outputs ofthese two current detection circuits I1 and 12 are fetched and anabnormality alarm is output when these two detection outputs are notwithin the respective permissible ranges for the aforementioned twocontrol modes.

As shown in FIG. 11a, which depicts one example, common potentialseparation circuit 25 for control input that is provided at the controlinput points of inverter control circuit 5 serves to input operatingsignals or signals from the various sensors, and has filter 25b whichremoves noise superimposed on these signals, and photocoupler 25a whichseparates the two common potentials.

As shown in FIG. 11b, which depicts one example, common potentialseparation circuit 26 for output that is provided at the control outputpoints of inverter control circuit 5 has photocoupler 26a whichseparates the two common potentials; and diode 26e, resistor 26f andfilter 26b, which prevent reverse current due to external noise. Theoutput signal is sent to the external circuits via relay 26c which opensand closes switch 26d.

The operation of the third embodiment so constituted need not beexplained in full since it is largely identical to that of the secondembodiment described above. The distinguishing characteristic of thisthird embodiment lies in the operation of the bidirectional DC-to-DCconverter. Namely, referring to FIG. 10, in low-voltage-to-high-voltageconversion mode, converter control circuit 24 gives switching controlsignals to low-voltage side switching elements Ta and Tb, and openshigh-voltage side switching elements Tc and Td. Under thesecircumstances, because the voltage applied to low-voltage siderectifying elements Da and Db, which are parallel-connected acrosslow-voltage side switching elements Ta and Tb, is a reverse voltage,said low-voltage side rectifying elements Da and Db do not operate. Onthe other hand, because the voltage applied to high-voltage siderectifying elements Dc and Dd, which are parallel-connected acrosshigh-voltage side switching elements Tc and Td (which are being keptopen), is a forward voltage, said high-voltage side rectifying elementsDc and Dd operate as rectifying elements.

In the high-voltage-to-low-voltage conversion mode, converter controlcircuit 24 gives switching control signals to high-voltage sideswitching elements Tc and Td, and opens low-voltage side switchingelements Ta and Tb. Under these circumstances, because the voltageapplied to high-voltage side rectifying elements Dc and Dd, which areparallel-connected across high-voltage side switching elements Tc andTd, is a reverse voltage, these elements do not operate. On the otherhand, because the voltage applied to low-voltage side rectifyingelements Da and Db, which are parallel-connected across low-voltage sideswitching elements Ta and Tb, is a forward voltage, said low-voltageside rectifying elements Da and Db operate as rectifying elements.

As has now been described, the storage means includes high-voltageelectrostatic capacitive circuit 20 directly connected to the DC side ofinverter circuit 4, and storage battery 22 with a low voltage equal tothe rated voltage of the ordinary electrical equipment. Accordingly, toprevent any danger to human beings, the low-voltage side commonpotential that constitutes one terminal of storage battery 22, and thehigh-voltage side common potential that constitutes one terminal ofelectrostatic capacitive circuit 20, are separated by means of thebidirectional DC-to-DC converter and by common potential separationcircuits 25 for control inputs and common potential separation circuits26 for outputs which are provided in inverter control circuit 5 andwhich are shown in FIGS. 11a and 11b. The common potential of invertercontrol circuit 5 is then connected to the high-voltage side commonpotential, and the low-voltage side common potential is connected to thebody potential of the motor vehicle.

As has now been explained, as well as providing a lightweight electricalpower supply for motor vehicles, this invention enables the utilizationefficiency of electrical energy to be improved. It therefore, makes itpossible to utilize a braking and auxiliary driving means in smallervehicles.

Moreover, because an electrostatic capacitive circuit is used, nomaintenance is required. It follows that the device can be distributedin dispersed fashion around a vehicle and can be sealed in an insulatingstructure, thereby ensuring human safety. Other effects include theability to find the quantity of stored charge accurately and inreal-time by means of voltage detection.

When used in conjunction with a battery, other effects of this inventioninclude the ability to start the internal combustion engine even whenhardly any stored charge is left in the electrostatic capacitivecircuit, and to prevent the supply of braking and auxiliary motive powerbecoming insufficient, which will occur when a large storage batteryfalls into disuse.

When a bidirectional DC-to-DC converter is utilized, this invention hasthe following effects: by controlling the bidirectional DC-to-DCconverter, the low voltage required for the general load circuits can begenerated and charging of the storage battery can be steadilymaintained. In addition, by separating the high-voltage side andlow-voltage side common potentials and thereby floating the high-voltageside common potential with respect to the vehicle body potential,electric shock due to a person touching the high-voltage side can beprevented.

We claim:
 1. Braking and auxiliary drive apparatus for an internalcombustion engine in a motor vehicle, comprising:a squirrel-cagepolyphase induction machine having a polyphase AC circuit, forcoupling]said squirrel-cage polyphase induction machine beingoperatively coupled to a rotary shaft of an internal combustion engine;an inverter circuit operatively coupled to said polyphase AC circuit ofsaid squirrel-cage polyphase induction machine; an electricity storagemeans comprising an electrostatic capacitive circuit operatively coupledto said inverter so that said inverter couples said electrostaticcapacitive circuit to said polyphase AC circuit by converting electricalenergy in both directions therebetween; a step-up/step-down converteroperatively coupled to said electrostatic capacitive circuit; a rotationsensor that detects a rotational speed of said rotary shaft; a storagebattery operatively coupled to said step-up/step-down converter so thatsaid step-up/step-down converter electrically connects said storagebattery to said electrostatic capacitive circuit, said storage batteryhaving a lower terminal voltage than a DC terminal voltage of saidinverter circuit; and a control circuit for controlling said invertercircuit, said control circuit operating in the following controlmodes:an initial charging mode wherein said electrostatic capacitivecircuit is charged with energy from said storage battery through saidstep-up/step-down converter, if said internal combustion engine is at astandstill; a starting mode wherein energy stored in said electrostaticcapacitive circuit is provided to said squirrel-cage polyphase inductionmachine as an AC current via said inverter circuit so that saidsquirrel-cage polyphase induction machine operates as an electric motor,if said internal combustion engine is being started; a deceleration modewherein said squirrel-cage polyphase induction machine operates anelectric generator by supplying an AC signal having a frequency that islower than a frequency corresponding to an actual speed detected by saidrotational sensor, said AC signal being provided to said electrostaticcapacitive circuit via said inverter circuit for charging saidelectrostatic capacitive circuit, if said vehicle is being braked; andan acceleration mode wherein said squirrel-cage polyphase inductionmachine operates an electric motor by supplying an AC signal having ahigher frequency than a frequency corresponding to an actual speeddetected by said rotational sensor, said electrostatic capacitivecircuit providing energy to said squirrel-cage polyphase inductionmachine via said inverter circuit, if said vehicle is being accelerated.2. Braking and auxiliary drive apparatus for an internal combustionengine in a motor vehicle, comprising:a squirrel-cage polyphaseinduction machine having a polyphase AC circuit, for coupling]saidsquirrel-cage polyphase induction machine being operatively coupled to arotary shaft of an internal combustion engine; an inverter circuitoperatively coupled to said polyphase AC circuit of said squirrel-cagepolyphase induction machine; an electricity storage means comprising anelectrostatic capacitive circuit operatively coupled to said inverter sothat said inverter couples said electrostatic capacitive circuit to saidpolyphase AC circuit by converting electrical energy in both directionstherebetween; a bidirectional DC-to-DC converter operatively connectedto said electrostatic capacitive circuit said bidirectional DC-to-DCconverter having switching elements and a control circuit forcontrolling a direction of energy transfer by controlling switching ofsaid switching elements; a rotation sensor that detects a rotationalspeed of said rotary shaft; a storage battery operatively coupled tosaid DC-to-DC converter so that said DC-to-DC converter electricallyconnects said storage battery to said electrostatic capacitive circuit,said storage battery having a lower terminal voltage than a DC terminalvoltage of said inverter circuit; and a control circuit for controllingsaid inverter circuit, said control circuit operating in the followingcontrol modes:an initial charging mode wherein said electrostaticcapacitive circuit is charged with energy from said storage batterythrough said DC-to-DC converter, if said internal combustion engine isat a standstill; a starting mode wherein energy stored in saidelectrostatic capacitive circuit is provided to said squirrel-cagepolyphase induction machine as an AC current via said inverter circuitso that said squirrel-cage polyphase induction machine operates as anelectric motor, if said internal combustion engine is being started; adeceleration mode wherein said squirrel-cage polyphase induction machineoperates an electric generator by supplying an AC signal having afrequency that is lower than a frequency corresponding to an actualspeed detected by said rotational sensor, said AC signal being providedto said electrostatic capacitive circuit via said inverter circuit forcharging said electrostatic capacitive circuit, if said vehicle is beingbraked; and an acceleration mode wherein said squirrel-cage polyphaseinduction machine operates an electric motor by supplying an AC signalhaving a higher frequency than a frequency corresponding to an actualspeed detected by said rotational sensor, said electrostatic capacitivecircuit providing energy to said squirrel-cage polyphase inductionmachine via said inverter circuit, if said vehicle is being accelerated.3. Braking and auxiliary drive apparatus for an internal combustionengine, comprising:a squirrel-cage polyphase induction machine having apolyphase AC circuit, for coupling]said squirrel-cage polyphaseinduction machine having a rotary shaft that is directly coupled to arotary shaft of the internal combustion engine; an inverter circuitoperatively coupled to said polyphase AC circuit of said squirrel-cagepolyphase induction machine; an electricity storage means comprising anelectrostatic capacitive circuit operatively coupled to said inverter sothat said inverter couples said electrostatic capacitive circuit to saidpolyphase AC circuit by converting electrical energy in both directionstherebetween; a control circuit that controls said inverter circuit suchthat in an acceleration mode, said squirrel-cage polyphase inductionmachine is used as an auxiliary driving means for said internalcombustion engine by providing a rotating magnetic field with a velocitythat exceeds a rotational speed of said internal combustion engine tosaid squirrel-cage polyphase induction machine, and in a decelerationmode, said squirrel-cage polyphase induction machine is used as abraking device for said internal combustion engine by providing arotating magnetic field with a velocity that is less than saidrotational speed of said internal combustion engine to saidsquirrel-cage polyphase induction machine; and wherein said invertercircuit includes a circuit which, in said acceleration mode, outputselectrical energy stored in said electricity storage means to saidsquirrel-cage polyphase induction machine as a polyphase AC output, andin said deceleration mode, outputs polyphase AC energy from saidsquirrel-cage polyphase induction machine to said electricity storagemeans; and a storage battery having a lower terminal voltage than a DCterminal voltage of said inverter circuit; a bidirectional DC-to-DCconverter connecting said storage battery to said electrostaticcapacitive circuit, said bidirectional DC-to-DC converter havingswitching elements and a control circuit for controlling a direction ofenergy transfer by controlling switching of said switching elements. 4.A braking and auxiliary driving means for a motor vehicle as set forthin claim 1, 2 or 3, and wherein a terminal voltage of said storagebattery corresponds to a rated voltage of standard electric equipment ofsaid motor vehicle.
 5. A braking and auxiliary driving means for aninternal combustion engine as set forth in claim 2 or 3, and wherein:alow-voltage side common potential constituting one terminal of saidcontrol circuit includes an initial charging mode, wherein saidelectrostatic capacitive circuit is charged with energy from saidstorage battery after conversion by said DC-to-DC converter; and abattery-charging mode wherein, if a terminal voltage of saidelectrostatic capacitive circuit exceeds a prescribed value, saidstorage battery is charged with stored electrical energy from saidelectrostatic capacitive circuit after conversion by said DC-to-DCconverter.
 6. A braking and auxiliary driving means for an internalcombustion engine as set forth in claim 5, wherein said low-voltage sidecommon potential is connected to a potential of said internal combustionengine.
 7. A braking and auxiliary driving means for an internalcombustion engine as set forth in claim 6, wherein said control modes ofsaid control circuit include an initial charging mode wherein saidelectrostatic capacitive circuit is charged with energy from saidstorage battery after conversion by said DC-to-DC converter; and abattery-charging mode wherein, if a terminal voltage of saidelectrostatic capacitive circuit exceeds a prescribed value, saidstorage battery is charged with stored electrical energy from saidelectrostatic capacitive circuit after conversion by said DC-to-DCconverter.
 8. A braking and auxiliary driving means for an internalcombustion engine as set forth in claim 6, further comprising anelectrically insulating material encasing said inverter circuit, controlcircuit and electrostatic capacitive circuit and a metal containerconnected to said vehicle body potential having said inverter circuit,control circuit and electrostatic capacitive circuit housed therein. 9.In respect of a braking and auxiliary driving means for an internalcombustion engine as set forth in claim 1:a braking and auxiliarydriving means for a motor vehicle characterised in that the controlmodes of the aforementioned control circuit include: an initial chargingmode wherein, with the aforementioned internal combustion engine atstandstill, the aforementioned electrostatic capacitive circuit ischarged with the energy of the aforementioned storage battery after thevoltage has been stepped up by a step-up/step-down converter; a startingmode wherein, when the aforementioned internal combustion engine isbeing started, energy stored in the aforementioned electrostaticcapacitive circuit is given to the aforementioned squirrel-cagepolyphase induction machine as an AC current via the aforementionedinverter circuit, and the aforementioned squirrel-cage polyphaseinduction machine is made to operate as an electric motor; adeceleration mode wherein, when the aforementioned motor vehicle isbeing braked, the aforementioned squirrel-cage polyphase inductionmachine is made to operate as an electric generator, and the output ACcurrent of the aforementioned squirrel-cage polyphase induction machineis supplied to the aforementioned electrostatic capacitive circuit as acharging current via the aforementioned inverter circuit; and anacceleration mode, wherein, when the aforementioned motor vehicle isbeing accelerated, the aforementioned squirrel-cage polyphase inductionmachine is made to operate as an electric motor, and energy stored inthe aforementioned electrostatic capacitive circuit is supplied via theaforementioned inverter circuit to the aforementioned squirrel-cagepolyphase induction machine as an AC current.
 10. Braking and auxiliarydrive apparatus for an internal combustion engine, comprising:asquirrel-cage polyphase induction machine having a polyphase AC circuit,for coupling]said squirrel-cage polyphase induction machine having arotary shaft that is directly coupled to a rotary shaft of the internalcombustion engine; an inverter circuit operatively coupled to saidpolyphase AC circuit of said squirrel-cage polyphase induction machine;an electricity storage means comprising an electrostatic capacitivecircuit operatively coupled to said inverter so that said invertercouples said electrostatic capacitive circuit to said polyphase ACcircuit by converting electrical energy in both directions therebetween;including said internal combustion engine and wherein: said rotary shaftof the aforementioned internal combustion engine and a rotary shaft ofthe aforementioned squirrel-cage polyphase induction machine aredirectly connected;] a control circuit that controls said invertercircuit such that in an acceleration mode, said squirrel-cage polyphaseinduction machine is used as an auxiliary driving means for saidinternal combustion engine by providing a rotating magnetic field with avelocity that exceeds a rotational speed of said internal combustionengine to said squirrel-cage polyphase induction machine, and in adeceleration mode, said squirrel-cage polyphase induction machine isused as a braking device for said internal combustion engine byproviding a rotating magnetic field with a velocity that is less thansaid rotational speed of said internal combustion engine to saidsquirrel-cage polyphase induction machine; and wherein said invertercircuit includes a circuit which, in said acceleration mode, outputselectrical energy stored in said electricity storage means to saidsquirrel-cage polyphase induction machine as a polyphase AC output, andin said deceleration mode, outputs polyphase AC energy from saidsquirrel-cage polyphase induction machine to said electricity storagemeans.
 11. A braking and auxiliary driving means for a motor vehicle asset forth in claim 1 or 10, and wherein:said control modes of saidcontrol circuit also include: a warm-up mode wherein, if internalcombustion engine is warming up, said squirrel-cage polyphase inductionmachine operates as an electric generator and an output AC current ofsaid squirrel-cage polyphase induction machine is supplied via saidinverter circuit to said electrostatic capacitive circuit as a chargingcurrent; and a supplementary charging mode wherein, if said internalcombustion engine is operating and a terminal voltage of saidelectrostatic capacitive circuit no greater than a prescribed value,said squirrel-cage polyphase induction machine operates as an electricgenerator, and said output AC current of said squirrel-cage polyphaseinduction machine is supplied via said inverter circuit to saidelectrostatic capacitive circuit as a charging current.